This invention relates to a process for the preparation of 6-fluoro-7-pyridyl-1,4-dihydroquinol-4-one 3-carboxylic esters and acids having antibacterial activity and to novel intermediates for use in said process.
U.S. Pat. Nos. 3,753,993 and 3,907,808 describe the preparation of 1,4-dihydro-1-(lower alkyl)-4-oxo-7-(3- or 4-pyridyl)-3-quinolinecarboxylic acids and esters from 3- or 4-(3-aminophenyl)pyridines through ring cyclization after reaction with an appropriate methylene malonate. Although the patents in general disclose compounds having a halogen in the phenyl part of the quinoline, it is noted that there are no examples of their preparation. The only examples are to 7-(substituted-pyridine)derivatives. The known methods for preparing pyridyl-aryl compounds usually convert a suitably substituted benzene derivative by b,uilding up the pyridine ring, as illustrated in the above two patents. These methods often require a considerable number of steps and they are not readily adaptable to the preparation of substituted analogs.